1. Field of the Invention
The invention relates to a resolver used to detect the rotation angle (rotational position) of a rotational shaft of a motor, or the like, and relates also to a resolver-rolling bearing unit.
2. Description of Related Art
A resolver is one type of angle detection devices for detecting the rotation angle (rotational position) of a rotational shaft, and includes a resolver stator and a resolver rotor. A resolver stator is an annular member having, at its inner peripheral face, a plurality of teeth (tooth portions) which are arranged at given intervals in the circumferential direction of the resolver stator. A coil is wound around each tooth. A resolver rotor is disposed on the radially inner side of the resolver stator with a clearance formed between the resolver stator and the resolver rotor, and is attached to a rotational shaft so as to be rotatable together with the rotational shaft (for example, refer to Japanese Patent Application Publications No. 2006-90511 and No. 2007-336714).
In a resolver described in Japanese Patent Application Publication No. 2006-90511, a resolver stator is press-fitted at its outer peripheral face to the inner peripheral face of a cylindrical case. With this structure, however, if there is a distortion or dimensional variation at a part of the inner peripheral face of the case, the radial positions of some of teeth formed at the inner peripheral face of the resolver stator may change. This may raise a possibility that a clearance between the resolver stator and a resolver rotor will not be appropriately set.
Japanese Patent Application Publication No. 2006-90511 (refer especially to FIG. 2) describes a resolver-rolling bearing unit. In this resolver-rolling bearing unit, a press-fit cylindrical portion is formed at an axial end of an outer ring of a rolling bearing, and the case is press-fitted, at its outer peripheral face, to the inner peripheral face of the press-fit cylindrical portion. Thus, the rolling bearing is fixed to the case. In this structure, the position of the press-fit cylindrical portion of the outer ring and the position of the resolver stator substantially overlap each other in the axial direction. Therefore, a distortion or the like, which is caused at the case when the case is press-fitted to the press-fit cylindrical portion of the outer ring, may directly affect the resolver stator. This may raise a possibility that a clearance between the resolver stator and the resolver rotor will not be appropriately set. Further, the outer ring is fixed to a housing of a motor, or the like, by fitting. If the housing thermally expands more than the outer ring does due to the use under a high-temperature environment, the interference of the outer ring is reduced. This may raise a possibility that the outer ring will run idle in the housing. This idle running may cause, for example, wear of the housing.
In a resolver described in Japanese Patent Application Publication No. 2007-336714, a resolver stator and a resolver rotor are provided as individual parts, and a rolling bearing that rotatably supports a rotational shaft is provided as an individual part that is separated from the resolver stator and the resolver rotor. The resolver stator, the resolver rotor, and the rolling bearing are attached to a housing of a motor, or the like, and the rotational shaft, individually. Therefore, handling each part of the resolver and each part of the rolling bearing is cumbersome, and attaching the resolver and the rolling bearing to the housing and the rotational shaft is also cumbersome. This may make it difficult to ensure a high accuracy in each assembly work, such as centering of each part.